Chang-Mo Ryu

Electron acceleration by a circularly polarized laser pulse in the presence of an obliquely incident magnetic field in vacuum

Laser-induced acceleration of an electron injected initially at an angle to the direction of a circularly polarized laser pulse in the presence of an obliquely incident magnetic field has been investigated. For a suitable position of the peak of the laser pulse, the external magnetic field exists at an angle such that it can be parallel to the magnetic field of the laser pulse. The electron gains considerable energy and retains it even after passing of the laser pulse in the presence of an optimum magnetic field in vacuum. The electron attains the maximum amount of energy at a particular angle of the incident magnetic field due to the betatron resonance.

Ion thermal pressure effects on dust ion acoustic solitary waves in a dusty plasma obliquely propagating to an external magnetic field

Effects of the isothermal ion pressure on the dust ion acoustic solitary waves (DIASWs) in a dusty plasma, which are obliquely propagating to an external magnetic field, are investigated based on the Sagdeev potential. It is found that as the ion temperature increases the speed of the DIASW increases. The increase is more effective for a higher value of the directional cosine lz. The small amplitude solutions of the Sagdeev potential Ψ(n) expanded up to δn3 and δn4, as was done in the previous study [Choi et al., Phys. Plasmas 12, 022304 (2005)], exhibit different behaviors with respect to the change in the ion temperature. The width and height of a double layer are found to decrease with the increase in the ion temperature for both the small and the large amplitude solutions.

Obliquely propagating ion acoustic solitary waves and double layers in a magnetized dusty plasma with anisotropic ion pressure

Obliquely propagating dust ion acoustic solitary waves and double layers in an external magnetic field is studied by using Sagdeev’s pseudo-potential technique. Anisotropic ion pressure is considered, which is defined by applying the Chew–Goldberger–Low theory. The Sagdeev pseudo-potential is derived considering the Poisson equation instead of the charge neutrality condition so that the length scales of the solitary waves and double layers may be shorter than the Debye length. The ranges of parameters for which solitary waves and double layers can exist are studied in detail.

Effects of broken time-reversal symmetry on transmission zeros in the Aharonov-Bohm interferometer

In this paper, we study the behavior of the transmission zeros in the closed Aharonov-Bohm (AB) interferometer with an embedded scattering center in one arm and the corresponding change in the transmission phase when the time-reversal symmetry is broken by magnetic fields. Specifically, we consider three embedded scattering centers: one discrete energy level, a double-barrier well, and a t stub. We find the following from our model study: (i) The transmission zeros are real when the AB flux is an integer or a half integer multiple of the flux quantum, and the transmission phase jumps by π at the zeros. (ii) The transmission zeros become complex or are shifted off the real-energy axis when the magnetic AB flux is not an integer or a half integer multiple of the flux quantum, and the transmission phase evolves continuously. (iii) The distance of the zeros from the real-energy axis or the imaginary part of the transmission zeros is sinusoidal as a function of the magnetic AB phase. We suggest the experimental setup which can test our results.

Nonlinear saturation of relativistic Weibel instability driven by thermal anisotropy

The present paper investigates nonlinear saturation of the relativistic Weibel instability by employing theory and a particle-in-cell simulation technique. It is found that the early phase of the instability is in excellent agreement with linear theory. Qualitative agreement with quasilinear prediction is also found. An analysis based on an alternative magnetic trapping saturation theory reveals that a relativistic formula leads to a substantial discrepancy between theory and simulation. However, excellent agreement is recovered in the nonrelativistic regime. The analysis of the Weibel instability beyond the quasilinear saturation stage reveals an inverse cascade process via a nonlinear decay instability involving electrostatic fluctuation.

Directional dependence of spin currents induced by Aharonov-Casher phase

We have calculated the persistent spin current of an open ring induced by the Aharonov–Casher phase. For unpolarized electrons there exist no persistent charge currents, but persistent spin currents. We show that, in general, the magnitude of the persistent spin current in a ring depends on the direction of the direct current flow from one reservoir to another. The persistent spin current is modulated by the cosine function of the spin precession angle. The nonadiabatic Aharonov–Casher phase gives anomalous behaviors. The Aharonov–Anandan phase is determined by the solid angle of spin precession. When the nonadiabatic Aharonov–Anandan phase approaches a constant value with the increase of the electric field, the periodic behavior of the spin persistent current occurs in an adiabatic limit. In this limit the periodic behavior of the persistent spin current could be understood by the effective spin-dependent Aharonov–Bohm flux.

Spin fluctuation and persistent current in a mesoscopic ring coupled to a quantum dot

We investigate the persistent current influenced by the spin fluctuations in a mesoscopic ring weakly coupled to a quantum dot. It is shown that the Kondo effect gives rise to some unusual features of the persistent current in the limit where the charge transfer between two subsystems is suppressed. Various aspects of the crossover from a delocalized to a localized dot limit are discussed in relation with the effect of the coherent response of the Kondo cloud to the Aharonov-Bohm flux.

Simulation and theory for two-dimensional beam-plasma instability

A comparative study of the dynamics of the electron beam-plasma system in two spatial dimensions is carried out by means of particle-in-cell (PIC) simulation and quasilinear theory. In the literature, the beam-plasma instability is usually studied with one-dimensional assumption. Among the few works that include higher-dimensional effects are two- and three-dimensional quasilinear theory and two-dimensional PIC simulations. However, no efforts were made to compare the theory and simulation side by side. The present paper carries out a detailed comparative study of two-dimensional simulation and quasilinear theory. It is found that the quasilinear theory quite adequately accounts for most important features associated with the simulation result. For instance, the particle diffusion time scale, the maximum wave intensity, dynamical development of the electron distribution function, and the change in the wave spectrum all agree quantitatively. However, certain nonlinear effects such as the Langmuir condensation phenomenon are not reproduced by the quasilinear theory. Nevertheless, the present paper verifies that the simple quasilinear theory is quite effective for the study of beam-plasma instability for the present choice of parameters.

Effects of spontaneous thermal fluctuations on nonlinear beam-plasma interaction

In this paper, the effects of nonvanishing plasma parameter 1∕nλDe3 on the nonlinear beam-plasma interaction process are discussed on the basis of numerical solutions of weak turbulence equation. The finiteness of the plasma parameter is directly related to the single-particle spontaneous fluctuation phenomena. It is shown that spontaneous fluctuations promote the Langmuir condensation effect, lead to a finite level of ambient turbulence, and enhance nonlinear mode coupling process.

QUANTUM WAVEGUIDE THEORY FOR TRIPLY CONNECTED AHARONOV–BOHM RINGS

Quantum interference effects for a mesoscopic loop with three leads are investigated by using a one-dimensional quantum waveguide theory. The transmission and reflection probabilities are analytically obtained in terms of the magnetic flux, arm length, and wave vector. Oscillation of the magnetoconductance is explicitly demonstrated. Magnetoconductance is found to be sharply peaked for certain localized values of flux and kl. In addition, it is noticed that the periodicity of the transmission probability with respect to kl depends more sensitively on the lead position, compared to the case of the two-lead loop.